Re: [PATCH 2/2] fs/lock: show locks taken by processes from another pidns

From: Andrey Vagin <avagin@virtuozzo.com>
To: Konstantin Khorenko <khorenko@virtuozzo.com>
Cc: Kirill Gorkunov <kgorkunov@virtuozzo.com>,
	Benjamin Coddington <bcodding@redhat.com>,
	Jeff Layton <jlayton@kernel.org>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Vasily Averin <vvs@virtuozzo.com>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] fs/lock: show locks taken by processes from another pidns
Date: Mon, 11 Jun 2018 21:53:31 -0700	[thread overview]
Message-ID: <20180612045330.GB8843@outlook.office365.com> (raw)
In-Reply-To: <20180608142712.32460-3-khorenko@virtuozzo.com>

On Fri, Jun 08, 2018 at 05:27:12PM +0300, Konstantin Khorenko wrote:
> Currently if we face a lock taken by a process invisible in the current
> pidns we skip the lock completely, but this
> 
> 1) makes the output not that nice
>     (root@vz7)/: cat /proc/${PID_A2}/fdinfo/3
>     pos:    4
>     flags:  02100002
>     mnt_id: 257
>     lock:   (root@vz7)/:
> 
> 2) makes it more difficult to debug issues with leaked flocks
>    if you get error on lock, but don't see any locks in /proc/$id/fdinfo/$file

3) breaks the CRIU project. criu reads fdinfo to dump file locks.

> 
> Let's show information about such locks again as previously, but
> show zero in the owner pid field.
> 
> After the patch:
> ===============
> (root@vz7)/:cat /proc/${PID_A2}/fdinfo/3
> pos:    4
> flags:  02100002
> mnt_id: 295
> lock:   1: FLOCK  ADVISORY  WRITE 0 b6:f8a61:529946 0 EOF
>

I think initially this was broken in this commit:

Fixes: d67fd44f697d ("locks: Filter /proc/locks output on proc pid ns")

Acked-by: Andrei Vagin <avagin@openvz.org>

Thanks,
Andrei

> Fixes: 9d5b86ac13c5 ("fs/locks: Remove fl_nspid and use fs-specific l_pid for remote locks")
> Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
> ---
>  fs/locks.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index bfee5b7f2862..e533623e2e99 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -2633,12 +2633,10 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
>  
>  	fl_pid = locks_translate_pid(fl, proc_pidns);
>  	/*
> -	 * If there isn't a fl_pid don't display who is waiting on
> -	 * the lock if we are called from locks_show, or if we are
> -	 * called from __show_fd_info - skip lock entirely
> +	 * If lock owner is dead (and pid is freed) or not visible in current
> +	 * pidns, zero is shown as a pid value. Check lock info from
> +	 * init_pid_ns to get saved lock pid value.
>  	 */
> -	if (fl_pid == 0)
> -		return;
>  
>  	if (fl->fl_file != NULL)
>  		inode = locks_inode(fl->fl_file);
> -- 
> 2.15.1
> 